The SN65HVD21A offers performance far exceeding typical RS−485 devices. In addition to meeting all requirements of the TIA/EIA−485−A standard, the device operates over an extended range of common-mode voltage, and has features such as high ESD protection, wide receiver hysteresis, and failsafe operation. This device is ideally suited for long-cable networks, and other applications where the environment is too harsh for ordinary transceivers.
The device is designed for bidirectional data transmission on multipoint twisted-pair cables. Example applications are digital motor controllers, remote sensors and terminals, industrial process control, security stations, and environmental control systems.
The device combines a 3-state differential driver and a differential receiver, which operate from a single 5-V power supply. The driver differential outputs and the receiver differential inputs are connected internally to form a differential bus port that offers minimum loading to the bus. This port features an extended common-mode voltage range making the device suitable for multipoint applications over long cable runs.
The SN65HVD21A allows up to 256 connected nodes at moderate data rates (up to 6 Mbps). The driver output slew rate is controlled to provide reliable switching with shaped transitions which reduce high-frequency noise emissions.
The receivers also include a failsafe circuit that provides a high-level output within 250 microseconds after loss of the input signal. The most common causes of signal loss are disconnected cables, shorted lines, or the absence of any active transmitters on the bus. This feature prevents noise from being received as valid data under these fault conditions. This feature may also be used for Wired-Or bus signaling.
The SN65HVD21A is characterized for operation over the temperature range of –40°C to 85°C.
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